Bearing clearance has a great influence on bearing life, temperature rise, noise, etc. Therefore, it is necessary to select the appropriate clearance according to the working conditions and performance requirements. The clearance of the bearing is divided into radial clearance and axial clearance, which respectively represent the displacement of one sleeve fixed and the other sleeve from one limit position to another limit position along the radial and axial directions. The radial clearance of the bearing includes the original clearance in the free state before the bearing is installed, the assembly clearance after the main shaft and the bearing seat are installed, and the working clearance formed under the load during operation. For ball bearings, the optimum working clearance is close to zero; for roller bearings, a small amount of working clearance can be maintained. In components requiring good support rigidity, the bearing should have a certain amount of preload. This is the determination principle of bearing radial clearance. In the national standard GB4604-93, the radial clearance of rolling bearings is divided into 5 groups, and the clearance values ​​are in order from small to large, of which group 0 is the standard clearance. Bearings that work under special conditions such as high temperature, high speed, low noise and low friction should choose a larger radial clearance; for precision spindle bearings, a smaller radial clearance should be used. It should be noted that the working clearance of the bearing after installation is smaller than the original clearance before installation, because the bearing has to bear a certain load to rotate, as well as the elastic deformation caused by the bearing fit and the load. For radial thrust ball bearings and tapered roller bearings, they are usually installed face-to-face or back-to-back, and the axial position of a certain bearing ring determines the internal clearance or preload. Starting from a zero clearance condition, the specified clearance can be obtained by adjusting the thickness of the shims on the bearing outer ring or by loosening or tightening the back nut on the shaft. There is a fixed relationship between the axial clearance and radial clearance of this type of bearing, and one of these values ​​is sufficient. When selecting bearing clearance, the following aspects should also be considered: 1. The working conditions of the bearing, such as load, temperature, speed, etc.; 2. Requirements for bearing performance, such as rotation accuracy, friction torque, vibration and noise, etc.; 3. When the bearing is in an interference fit with the shaft and the housing hole, the bearing clearance is reduced; 4. When the bearing is working, the temperature difference between the inner and outer rings causes the bearing clearance to decrease; 5. The bearing clearance is reduced or increased due to the different expansion coefficients of the shaft and housing materials; 6. Due to the large temperature difference between the inner and outer rings of the bearing, the deep groove ball bearing needs to bear a large axial load or need to improve the self-aligning performance, and it is required to increase the limit speed and reduce the bearing friction torque and other occasions; 7. When the basic group cannot meet the use requirements, the auxiliary group clearance should be selected. The large clearance auxiliary group is suitable for the interference fit between the bearing and the shaft and the housing hole, and the small clearance auxiliary group is suitable for the occasions that require higher rotation accuracy, the axial displacement of the housing hole needs to be strictly controlled, and the vibration and noise need to be reduced .